1. Field of the Invention
The present invention relates to a method of regulating a cooling fan. More particularly, the present invention relates to a method for regulating the fan speed automatically so that the cooling performance is increased and a balance between the cooling efficiency and the noise of the cooling fan is achieved.
2. Description of the Related Art
A conventional cooling system is normally categorized into an air-cooling type and a water-cooling type. Using a notebook computer as an example, all of the central processor, the north bridge chip and the graphic chip on a main board are integrated circuit (IC) chips. In general, integrated circuit (IC) chips are the major sources of heat during operations in computer. To rapidly carry the heat generated by the IC chips away during a high-speed operation, and allow the IC chips to be operated for a long period, conventionally, a heat sink is directly attached to the backside of the IC chips. The heat sinks are normally fabricated using metallic or ceramic material with a high thermal conductivity.
In most notebook or other computer systems, it is insufficient to conduct the heat generated from the IC chips by only using the heat sink. Then it is necessary to include an additional cooling fan in the system to produce a cooling air flow, which flows toward an air outlet for dissipating heat to outside. It should be noted that an air-cooled module utilizes both a stream of cooling air from a fan and the large heat-dissipating area of the heat sink to increase the cooling performance. To provide a sufficiently strong air stream through a cooling fan, the wind-cut noise due to rotation of fan is accordingly produced. Furthermore, the air steam may produce a phenomenon of local high temperature close to the air outlet after absorbing a large quantity of heat from the operating ICs. When the air inlet or the air outlet is blocked causing a poor air circulation, the operating temperature inside the system easily becomes over high, causing an occurrence of damage. Once the temperature of internal IC chips or other internal devices exceed the specified operating range, computational error or temporary failure of the system may occur in the main board.
As a result, one major research topic in the minds of the manufacturers is to provide a means of regulating the fan speed of the cooling fan so that the efficiency of the cooling fan is increased and yet prevent the temperature of the thermal sources (for example, IC chips) from being over high, causing damage. With respect to the control of fan speed of fan, conventionally, the fan speed of the fan is simply regulated according to a relationship curve between the temperature of the thermal source and the voltage supplied to the cooling fan. However, if the system does not have a mechanism for detecting the difference between the actual fan speed of the fan and a prescribed fan speed but provides a voltage to the fan purely according to the relationship between the supplied voltage of the fan and the temperature of the thermal source, the cooling fan may rotate faster than the specification and waste electricity. On the other hand, if the system has a mechanism for detecting and regulating the actual fan speed of the fan and the prescribed fan speed, then the actual fan speed of the cooling fan is adjusted in a single operation to the prescribed fan speed when the fan reaches the fan speed regulating point. As an often result, the thermal source may continuously rise to a temperature close to the threshold temperature and shortens the lifetime of the thermal source. Moreover, the noise due to the sudden increase in the fan speed of the cooling fan may also bother the user.
FIG. 1 is a flow chart showing the steps in a Taiwanese patent No. 564341 having the title ‘a fan speed control device and a method for controlling the fan speed of a fan’. As shown in FIG. 1, the method comprises the following steps. In step 302, a temperature sensor detects a temperature and outputs a corresponding temperature signal. In step 304, a processing unit receives the temperature signal and exports a corresponding prescribed fan speed for the fan. In step 306, a control unit receives the prescribed fan speed value and transmits a corresponding regulating signal to the fan. In step 308, the control unit checks the difference between the actual fan speed of the fan and the prescribed fan speed. In step 310, the control unit accurately controls the fan speed of the fan according to the difference between the actual fan speed and the prescribed fan speed of the fan. However, the drawback of this method is that the actual fan speed of the fan is adjusted to the prescribed fan speed in a single operation. Hence, the temperature of the thermal source will continue to rise for a short period of time before it is balanced with the heat-dissipating rate. Moreover, the one-step adjustment from the actual fan speed of the fan to the prescribed fan speed can easily lead to a sudden burst of acoustic noise that may bother the user of the computer system.